A EMI ferrite can help. Pull all the wires a few times through it.I spent quite a lot of time trying to tune the transmiter, but was foiled by its sensitivity to stray capacitance. Just placing my hand near the PCB, the power wires, or especially the MP3 player caused the frequency to shift. Of course the power wires are too long waving in the breeze, but the cable from the MP3 player is shielded.
What sort of assembly error might I have made that would cause this frequency instability? And are the two variable capacitors normally interactive?
When I just take the USB cable in my hand, the radio starts to hiss with white noise. Approaching the circuit does not change so much, since the coils have ferrites. This makes them insensible to hand waiving.